Interactive computer-assisted surgical system and method thereof

ABSTRACT

A computer-assisted surgical system and method are described herein. The computer-assisted surgical system comprises a computer including three-dimensional models of anatomical structures and a user interface including a position sensing system to register in real-time the relative positions of the anatomical structures of interest and of a surgical tool. Interactions between the tool and the anatomical structure are displayed on a monitor using the three-dimensional models. Multi-view display, transparency display and use of cutting planes allow the surgeon to visualize the interaction between the tool and the anatomical structures any time during the surgical procedure. The system can also predict the constraint on anatomical structures before surgery.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of U.S. Provisional PatentApplications serial No. 60/087,089 and Ser. No. 60/087,091, both filedMay 28, 1998, and is a divisional application of U.S. application Ser.No. 09/322,398 filed May 28, 1999.

FIELD OF THE INVENTION

The present invention relates to computer-assisted surgical systems.More specifically, the present invention is concerned with aninteractive computer-assisted surgical system and method thereof.

BACKGROUND OF THE INVENTION

Computer-assisted surgical systems are used to help doctors during asurgical procedure. Initially, these systems were only displaying statusand data on the patient's physical condition. Eventually,computer-assisted surgical systems have evolved to allow real-timeinteraction between the surgeon procedures and the computer datadisplayed. In recent years, computer-assisted surgical systems begandisplaying computer generated models of the anatomical structures ofinterest to help the surgeon visualize the surgical procedure beingperformed.

One such system has been described by Willie WILLIAMSON, Jr. in U.S.Pat. No. 5,769,092, issued on Jun. 23, 1998. In this patent, Williamsonteaches a computer-assisted system to help perform a hip replacement.The system allows the surgeon to interact with three-dimensional modelsof the relevant bones to select an appropriate replacement strategy. Afirst drawback of Williamson's system is that there is no registrationof the anatomical structures of interest and thus, these anatomicalstructures must be adequately immobilized in order to visualize theinteraction between the structures and a robotic arm. The immobilizationof the anatomical structures renders the intra-operating room planningdifficult, since no trial movements can be performed on the immobilizedstructures. Furthermore, only the movements of the robotic arm arereproduced on the display monitor and the interaction is performed onlyon two-dimensional images of the anatomical structures. Finally,Williamson's system does not allow the visualisation of transparentthree-dimensional models of the anatomical structures.

In the U.S. Pat. No. 5,682,886, issued on Nov. 4, 1997, Scott L. DELP etal., propose a computer-assisted surgical system that overcomes somedrawbacks of Williamson's system. Delp teaches the interaction of asurgical tool with three-dimensional models of the anatomical structuresof interest. However Delp's system does not allow real-time update ofthe positions of both the surgical tool and the three-dimensionalmodels. Furthermore the registration process requires a lot of inputsfrom the surgeon. Another drawback of Delp's system is that thethree-dimensional models do not appear partially transparent on thedisplay monitor. Thus, the anatomical structures may obstruct the viewof the tool, depending on the relative position of the tool and theanatomical structures or the tool may simply be overlaid over thethree-dimensional model, providing partial occlusion of the structures.As discussed hereinabove with respect to Williamson's system, Delp'ssystem does not allow intra-operating room planning.

Improved computer-assisted surgical system and method are thusdesirable.

OBJECTS OF THE INVENTION

An object of the present invention is therefore to providecomputer-assisted surgical system and method free of the above mentioneddrawbacks of the prior-art.

Another object of the invention is to provide computer-assisted surgicalsystem and method that allow real-time registration of a surgical toolon transparent three-dimensional models of anatomical structures.

Still another object of the present invention is to providecomputer-assisted surgical system and method that allow real-timedisplay of the relative positions of transparent three-dimensionalmodels of anatomical structures and of a surgical tool.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there isprovided an interactive surgical system to assist a surgery on at leastone anatomical structure, the system comprising:

a tool;

a computer, including a three-dimensional model of each of the at leastone anatomical structure and a three-dimensional model of the tool;

an output device connected to the computer; the output device beingconfigured to display the model of each of the at least one anatomicalstructure and the model of the tool; and

a position sensing system connected to the computer; the positionsensing system being configured to register the position of the tool andthe position of each of the at least one anatomical structure andtransferring the positions to the computer;

whereby, in operation, the computer, using the positions of the tool andof the at least one anatomical structure, is configured to determinevirtual positions of the models of each of the at least one anatomicalstructures and of the tool and to control the output device to displaythe models of each of the anatomical structure and of the tool at theirrespective virtual positions; the three-dimensional model of each of theat least one anatomical structure being so displayed as to appearpartially transparent.

According to another aspect of the present invention, there is providedan interactive user interface for a computer system to assist a surgeryon an anatomical structure, the user interface comprising:

a tool;

an output device connected to the computer; the output device beingconfigured to display a three-dimensional model of each of the at leastone anatomical structure and a three-dimensional model of the tool; and

a position sensing system connected to the computer; the positionsensing system being configured to register the position of the tool andthe position of each of the at least one anatomical structure and totransfer these positions to the computer;

whereby, in operation, the computer, using the positions of the tool andof the at least one anatomical structure, is configured to determinevirtual positions of the models of each of the at least one anatomicalstructures and of the tool and to control the output device to displaythe models of each of the anatomical structure and of the tool at theirrespective virtual positions.

According to another aspect of the present invention, there is provideda method to assist a surgical procedure on at least one anatomicalstructure, the method comprising:

providing a position sensing system;

providing a tool to perform a surgical procedure on the at least oneanatomical structure;

using the position sensing system to register the relative position ofthe tool and of each of the at least one anatomical structure;

using the relative position of the tool and of each of the at least oneanatomical structure to compute respective virtual positions of each ofthe at least one anatomical structure and of the tool;

providing an output device;

displaying on the output device a first view including a transparentthree-dimensional computer model of each of the at least one anatomicalstructure and a three-dimensional computer model of the tool at therespective virtual positions.

According to yet another aspect of the present invention, there isprovided a method of determining the appropriate position of a surgicalimplant on at least one anatomical structure, the method comprising:

identifying a possible position for the implant on the at least oneanatomical structure;

registering the possible position for the implant and the position ofeach of the at least one anatomical structure;

creating a computer models of each of the at least one anatomicalstructure with the implant;

placing the at least one anatomical structure in at least one position;

registering the at least one position of the anatomical structure; and

using the at least one registered position to simulate constraints on atleast one of the at least one anatomical structure and the implant;

wherein the appropriate position is one of the at least one positionwhere the simulated constraint lies in a predeterminate acceptablerange.

Finally, according to another aspect of the present invention, there isprovided a computer-assisted surgical system to assist in theinstallation of an implant on at least one anatomical structure, thesystem comprising:

a tool to identify a possible position for the implant on the at leastone anatomical structure;

a computer including models of each of the at least one anatomicalstructure and of the implant;

a position sensing system connected to the computer; the positionsensing system being configured to register the possible position forthe implant with respect to at least one position of each of the atleast one anatomical structure and to transfer the positions to thecomputer; and

whereby, in operation, the computer simulates constraints for each ofthe at least one position of each of the at least one anatomicalstructure;

wherein an appropriate position of the implant is one of the at leastone position where the simulated constraint lies in a predeterminateacceptable range.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non restrictivedescription of preferred embodiments thereof, given by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a bloc diagram of an interactive computer-assisted surgicalsystem according to an embodiment of the present invention;

FIG. 2 is a schematic perspective view of a surgical tool and of a humanknee with reference clamps mounted thereto;

FIG. 3 is a schematic view of the interactive computer-assisted systemof FIG. 1 without the position sensing system;

FIG. 4 is a screen shot illustrating different points of view ofthree-dimensional models of anatomical structures displayed by thesystem of FIG. 1; and

FIG. 5 is a screen shot illustrating the interaction betweenthree-dimensional models of an anatomical structure and of a surgicaltool, as displayed by the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 1 of the appended drawings, an interactivecomputer-assisted surgical system 10 to perform a surgical procedure onanatomical structures will be described.

The system 10 comprises a computer 12 having a memory (not shown), astoring device 14 and a user interface 15. The user interface 15includes input devices 16, an output device in the form of a displaymonitor 18, a surgical tool 20 and a position sensing system 22.

The storing device 14 is used to store three-dimensional models of thesurgical tool 20 and of the anatomical structures, in this case, in theform of a femur 24 and a tibia 26, (see FIG. 2) on which a surgicalprocedure is to be performed. The storing device 14 can take any formwell known by a person of ordinary skills in the art: a hard disk drive,a disk drive, a CD-ROM drive, another computers memory, etc. The storingdevice 14 can be directly connected to the computer 12 via conventionalperipheral connectors, such as, for example, cables or an infraredconnection, or remotely via a computer network, such as, for example,the Internet.

In a preferred embodiment of the present invention, the input devices 16are in the form of a keyboard and a mouse. The input devices 16 allowthe user to enter commands to the computer 12, in order, for example, toselect display options. Although the system 10 is described with twoinput devices 16, only one can be used without departing from the spiritof the present invention. The input devices 10 can also take otherforms, such as, for example a touch screen or a voice recognitionsystem.

Although the present invention is described with a display monitor asthe output device 18, a person of ordinary skills in the art canconceive a similar system, using another type of output device 18, suchas, for example, three-dimensional display goggles, without departingfrom the spirit of the present invention.

The surgical tool 20 can be, for example, an awl, a screwdriver toinstall, for example, an artificial ligament, or any tool used insurgical procedures.

Turning briefly to FIG. 2 of the appended drawings, the position sensingsystem 22 will be described in further details. The position sensingsystem 22 includes a position sensing device, in the form of a videocamera (not shown), connected to the computer 12 via conventionalconnectors and reference clamps 28 and 30, secured respectively to thepatient's femur 24 and tibia 26. Position sensing systems are believedwell known to persons of ordinary skills in the art, and thus, will nowbe described only briefly.

The reference clamps 28 and 30 include bended rods 32,34 and referenceassemblies 36 and 38, secured to their respective rods 32 and 34.Reference assemblies 36 and 38 are of different shapes so that they canbe discriminated by the computer 12. Each of reference clamps 28 and 30,also includes mounting brackets 40 (only one shown) to adequately securethe reference clamps to the tibia 24 and the femur 26, using smallsurgical screws 41 (only two shown).

Similarly, a reference assembly 42 is secured by welding to the surgicaltool 20 via a bended rod 44. It is to be noted that the referenceassembly 42 may, alternatively, include a mounting bracket to secure thereference assembly 42 on other surgical tools.

The operation of the position sensing system 22 will now be described.The camera is used to capture and to transfer to the computer 12 theimage of the reference assemblies 36, 38 and 42 during the surgicalprocedure. A registration algorithm, including conventional registrationmethod, is used to convert the real-time image in relative positionbetween each of the reference assemblies 36, 38 and 42. Since theposition, shapes and size of each reference assemblies 36, 38 and 42 areknown to the computer 12, the relative position of the surgical tool 20with respect to the anatomical structures 24 and 26 may be calculated.

The position sensing system 22 may also include a dedicated processor(not shown) that can determine the relative positions of the referenceassemblies 36, 38 and 42 and/or the relative positions of the surgicaltool 20 and anatomical structures 24 and 26 before sending thatinformation to the computer 12.

Other well known position sensing systems, such as, for example, amagnetic position sensing system, can also be used. In such a system,the camera is advantageously replaced by a magnetic field sensor and thereference assemblies are advantageously replaced by magnetic fieldemitters.

It is to be noted that it may be advantageous to include a connectionbetween the surgical tool 20 and the position sensing system 22, whenusing certain position sensing systems 22.

It is also to be noted that, if the surgical tool 20 includes movingparts, individual reference assemblies must be secured to each of thosemoving parts in order to enable the display of relative positions.

Turning now to FIGS. 3,4 and 5 of the appended drawings, the generalfeatures of a computer-assisted surgical method according to an aspectof the present invention will be described.

The first step of the method is to provide the computer 12 withthree-dimensional models of the tibia 24, the femur 26 and the surgicaltool 20. These models are transferred from the storing device 14 to thecomputer memory. The three-dimensional models could have been obtained,for example, from two-dimensional slice images of the anatomicalstructures of interest, using three-dimensional reconstruction systems.Three-dimensional reconstruction systems are believed well known by aperson of ordinary skills in the art and thus will not be describedfurthermore. Other means can also be used to provide three-dimensionalmodels of the anatomical structures and of the surgical tools, withoutdeparting from the spirit of the present invention. The slice images canbe obtained, for example, by scanning the anatomical structures with aCT or a MRI scanner.

The second step is to calibrate the surgical tools 20 and the referenceclamps 28 and 30. For example, this is accomplished by the computer 12,by performing transformations, first, from the reference assembly 42 tothe tip of the surgical tool 20 and second, by selecting referencepoints on the three-dimensional models of the anatomical structures 24,26 and by identifying the corresponding points on the anatomicalstructures 24 and 26. Of course, other calibration protocols could beused.

During the surgical procedure, the position sensing system 22 will firstregister the positions and orientations of the reference assemblies36,38 and 42 in the coordinate system of the position sensing system(represented by the axes X,Y and Z in FIG. 2). Then the orientations andpositions of the surgical tool 20, the tibia 24 and the femur 26 aretransformed into virtual orientations and position in the referencesystem of the three-dimensional models, represented by the axes X′, Y′and Z, in FIG. 3. The three-dimensional models of the tool 20 and of theanatomical structures 24 and 26, denoted 20′, 24′ and 26′ in FIGS. 3-5,are then reproduced on the display monitor 18 in their new orientationsand at their new positions in the computer reference system.

The registration process by the position sensing system 22 and theregeneration of the image on the display monitor 18 are performed at arate sufficient to allow real-time display and interaction with thethree-dimensional models 24′ and 26′. The display is said to be inreal-time, since movement of the models is perceived as beingcontinuous, without flicker effect, and synchronized with the movementsof the anatomical structures 24, 26 and of the surgical tool 20.

The computer 12 is programmed to allow visualization of the anatomicalstructures 24′ and 26′ and of the surgical tools 20′ as it would be seenfrom different points of view. FIG. 4 of the appended drawingsillustrates four such views that can be simultaneously displayed on thedisplay monitor 18. The different points of view can be selected usingthe input devices 16.

The computer 12 is also programmed to display the anatomical structures24′ and 26′ as translucent (partially transparent) objects. The surgeoncan therefore always visualize the interaction between the surgical tool20 and the anatomical structures 24′ and 26′ since the surgical tool 20is never occluded by the anatomical structures 24′ and 26′. Softwareprograms that allow visualization of translucency and visualization ofthree-dimensional objects from different points of view are believedwell known by a person of ordinary skills in the art and will not bedescribed in further details.

In order to illustrate other features of the method of the presentinvention, a method of planning the installation of a surgical implant,while the patient is under sedation, using the system 10 will now bedescribed. The example chosen to illustrate the method is thereplacement of the Anterior Cruciate Ligament (ACL) of the knee by anartificial ligament.

It is well known by surgeons specialized in knee surgery that theartificial ligament that joints the femur to the tibia should be placedin such a way that it respects an isometry constraint. The presentsystem allows to virtually position a virtual ligament 50 in order toassess such constraint prior to the surgical procedure.

The surgeon uses the surgical tool 20, in the form of an awl, toidentify on the patient's tibia 24 and femur 26 the two points 46 and 48where he believes he should place the artificial ligament. From thosetwo points, a virtual model of the ligament 50 is created by thecomputer 12 and displayed on the monitor 18 with the models of the tibia24′ and femur 26′. (It is to be noted that the calibration stepdescribed hereinabove must be performed before the planning procedure.)As will become apparent upon reading the description of the followingexample, the planning procedure makes use of the features of the abovedescribed system and method.

The surgeon then flexes the patient's knee in order to obtain a set ofposition measurements. As it has been described hereinabove, thepositions of the tibia 24 and of the femur 26 will be determined by thecomputer 12 and displayed as tibia 24′ and femur 26′ onto the monitor18.

According to these positions, the computer 12 will calculate thedistance between the two specified points at different flexion angles. Amessage is then displayed on the monitor 18, informing the surgeonwhether or not the isometry constraint is respected. If the constraintis not within a pre-specified tolerance, the surgeon may change theproposed artificial ligament position and perform another leg flexion toverify isometry. Once a position is found satisfying, the surgeon canuse the system 10 to perform the surgical procedure. More specifically,the surgeon can visualize the positions of the two points 46 and 48 onthe three-dimensional computer models displayed on the monitor to guidehim while drilling the holes that will be used to fix the artificialligament 50.

Turning now to FIG. 5 of the appended drawings, other features of thesystem and method, according to the present invention, will bedescribed.

FIG. 5 illustrates the use of the interactive computer -assistedsurgical system 10 to perform a surgical procedure on a lumbar vertebra52.

One can see in FIG. 5 four different views 60, 62, 64 and 66 of thethree-dimensional models of a lumbar vertebra 52 and of the surgicaltool 20. In this example, the surgical tool is in the form of ascrewdriver.

Again, the use of transparency to display the three-dimensional model ofthe anatomical structure, here in the form of a lumbar vertebra 52,allows the surgeon to visualize the tip of the surgical tool 20′, eventhough it is inserted in one of the cavities of the lumbar vertebra 52.

In addition to select different view points and display simultaneouslythe three-dimensional models according to those views, using the inputdevice 16, the surgeon can also select cutting planes (see line 54 and56 on view 66 of FIG. 5) from which the anatomical structure is to beseen. The use of the cutting planes 54 and 56 indicates thecorrespondence between different views of the same anatomicalthree-dimensional model and thus helps the surgeon in performingsurgical navigation. For example, view 62 is taken from line 56.

According to a preferred embodiment of the present invention, it ispossible for the surgeon to choose the transparency intensity, rangingfrom opacity to disappearance of the models, used to display thethree-dimensional models of the anatomical structure 52.

It is to be noted that it is possible to display simultaneously two andthree-dimensional representations and views of the anatomical structuresand of the surgical tool without departing from the spirit of thepresent invention. The number of views displayed simultaneously may alsovary.

In a preferred embodiment of the present invention, a mouse is used toselect view points and cutting planes on the three-dimensional model ofthe anatomical structures. Of course, other input devices could be used.

The anatomical structure can be any part of the human anatomy from whicha computer three-dimensional model can be obtained. The structure musthowever have sufficient rigidity to allow registration of its position.

Although the present invention has been described hereinabove by way ofpreferred embodiments thereof, it can be modified, without departingfrom the spirit and nature of the subject invention as defined in theappended claims.

What is claimed is:
 1. A computer-assisted surgical system to assist inthe installation of an implant on at least one anatomical structure,said system comprising: a tool to identify a possible position for theimplant on the at least one anatomical structure; a computer includingmodels of each of the at least one anatomical structure and of theimplant; a position sensing system connected to said computer; saidposition sensing system being configured to register said possibleposition for the implant with respect to at least one position of eachof the at least one anatomical structure and to transfer said positionsto said computer; and whereby, in operation, said computer simulatesconstraints for each of said at least one position of each of the atleast one anatomical structure; wherein an appropriate position of theimplant is one of said at least one position where said simulatedconstraint lies in a predeterminate acceptable range.
 2. Acomputer-assisted surgical system as recited in claim 1, wherein saidtool is selected from the group consisting of an awl and a surgicalscrewdriver.
 3. A computer-assisted surgical system as recited in claim1, further comprising a storing device, connected to said computer; saidstoring device being configured to store at least one of said model ofthe at least one anatomical structure and of said surgical tool.
 4. Aninteractive surgical system as recited in claim 3, wherein said storingdevice is taken from the group consisting of a disk drive, a CD-ROMdrive, a hard disk drive and a computer memory.
 5. An interactivesurgical system as recited in claim 3, wherein said storing device isremotely connected to the computer via a computer network.
 6. Aninteractive surgical system as recited in claim 1, wherein said positionsensing system includes: at least one magnetic field emitter secured tothe at least one anatomical structure; a magnetic field emitter securedto said tool; and a magnetic field sensor to capture and to transfer tosaid computer the signal of said field emitters of said tool and of theat least one anatomical structure; wherein said computer uses saidsignals to determine the position of said anatomical structure and theposition of said tool.
 7. An interactive surgical system as recited inclaim 1, wherein said position sensing system includes: at least onereference assembly secured to the at least one anatomical structure; areference assembly secured to said tool; and a camera to capture and totransfer to said computer the image of s aid reference assemblies onsaid tool and on the at least one anatomical structure; said computerusing said image to determine the position of said anatomical structureand the position of said tool.
 8. An interactive surgical system asrecited in claim 1, wherein said output device is selected from thegroup consisting of a display monitor and three-dimensional displaygoggles.
 9. A method of determining the appropriate position of asurgical implant on at least one anatomical structure, said methodcomprising: identifying a possible position for the implant on the atleast one anatomical structure; registering said possible position forthe implant and the position of each of the at least one anatomicalstructure; creating a computer models of each of the at least oneanatomical structure with the implant; placing the at least oneanatomical structure in at least one position; registering said at leastone position of the anatomical structure; and using said at least oneregistered position to simulate constraints on at least one of the atleast one anatomical structure and said implant; wherein the appropriateposition is one of said at least one position where the simulatedconstraint lies in a predeterminate acceptable range.
 10. A method ofdetermining the appropriate position of a surgical implant as recited inclaim 9, further comprising displaying on an output device said computermodels of each of the at least one anatomical structure with theimplant.